As is well known, microparticles such as cells typically have different physical property values indicating electrical properties such as conductivity, dielectric constant, and permittivity, depending on the type, the conditions, and the like of the microparticles. For example, the conductivity of extracellular fluid and intracellular fluid for muscle cells and nerve cells is higher than that for skin cells with less moisture. Furthermore, in the measurement of the dielectric constant of cells by frequency sweep, the dielectric relaxation properties change with the form of the cells.
In the related art, an apparatus for detecting the impedance of microparticles flowing between a pair of electrodes disposed in a channel has been proposed as a technique for identifying individual microparticles according to such electrical properties (see Patent Literature 1). In addition, dielectric cytometry apparatuses for measuring the dielectric spectrum of microparticles flowing in a microchannel have been also proposed (see, for example, Patent Literatures 2 and 3).
In the dielectric cytometry apparatus described in Patent Literature 2, a fluid device having a narrow part in a channel and electrodes adjacent to the narrow part is used to improve the measurement accuracy. In the dielectric cytometry apparatus described in Patent Literature 3, a branched path is provided downstream of a narrow part in a channel of a fluid device, an electric field is applied to cells that have passed through the narrow part based on the information on the complex dielectric constant measured, and the direction of cell flow is controlled by dielectrophoresis to sort the cells.